Currently, a problem exists when an aircraft encounters conditions that could cause ice accretion on an airfoil. The airfoil is the two-dimensional cross-section of a wing or tail of which a control surface, such as on a flap, rudder or elevator is a part. An ice shape can form, creating a reduction in lift, increased drag, change in pitching and hinge moments and a loss of control of the aircraft. Performance is affected by altering the pressure distribution over the airfoil. For example, a premature airfoil stall may occur and can result from a steep angle of attack, a large flap deflection or a high ice ridge. The pressure acting on the upper surface of the flap is reduced and an upward unsteady force is imposed on the flap and acts to deflect the flap in that direction. The flap is essentially sucked upward by the lower pressure.
This abrupt ice-induced flow separation can lead to a sudden significant change in hinge moment, leaving insufficient time for the pilot to react correctly. Such occurrences have led to aircraft accidents in the past. Therefore, it is desirable to sense impending problems and to develop systems to correct or protect against them before a crash becomes inevitable.
The Ice Protection System or IPS, is currently being used to protect planes from ice accretion. IPS often combines de-icing techniques and anti-ice systems to provide aircraft protection. However, it is impractical for the IPS to be able to anti-ice the entire aircraft, and a situation may arise where such a system fails.
Due to this concern, another level of protection is under consideration to add to the current IPS, which would increase in-flight pilot awareness of icing effects by monitoring and possibly predicting degraded aerodynamic performance. The systems under development thus far detect the presence and extent of separated flow. Such flow unsteadiness can be sensed by measurement of surface pressure or velocity fluctuations as a function of time.
One example of such a sensor is the Aircraft Icing Performance Monitoring Systems, AIMS. AIMS measures pressure fluctuations on the low-pressure side of the wing. The Stall Warning Plus system also measures pressure by use of high-frequency solid-state pressure sensors. It senses contamination by monitoring both the fluctuating and steady components of local velocity. Another device collects time-dependent pressure measurements by an array of differential pressure sensors.
Each of these systems monitor potential contamination by measuring surface pressure fluctuations. However, these sensors only measure ice effects at a single point on the surface. Also, since these sensors rest on an outside surface of the aircraft, they are susceptible to environmental wear and may be plugged by ice or damaged by a foreign object.
Therefore, there is a need for an icing sensing device which measures the integrated effect of ice over an entire area of concern. Also, there is a need for a sensor which is resistant to operational and environmental wear, such as being damaged by ice or other foreign objects.
Accordingly, it is an object of the present invention to provide a new and improved aircraft surface contamination sensor and method which measures the integrated effect of ice over an entire area of concern.
Yet another object of the present invention is to provide a sensor which is resistant to operational and environmental wear, such as being plugged by ice or damaged by other foreign objects.
Another object of the present invention is to warn a pilot or operator of potentially unsafe conditions before they occur, giving the pilot time to change controls of the aircraft.